The present invention relates generally to power conditioning systems for driving motors and, more particularly, to an integrated power conditioning system for delivering power suitable for driving a motor that may be enclosed in a common housing.
Power plants are linked to power consuming facilities (e.g., buildings, factories, etc.) via utility grids designed so as to be extremely efficient in delivering massive amounts of power. To facilitate efficient distribution, power is delivered over long distances as fixed frequency three-phase alternating current (AC) power.
Despite being efficiently distributable, fixed frequency AC power is often not suitable for end use in consuming facilities. In many applications, the power delivered by the utility must be converted or “conditioned” to a useable form. For example, motors and their associated loads are one type of common inductive load employed at many consuming facilities that require power conditioning.
To this end, typical power “conditioning” systems configured to condition power for motor systems include AC-to-DC (direct current) rectifiers that convert the utility AC power to DC power applied to positive and negative DC buses (i.e. across a DC link) and an inverter linked to the DC link that converts the DC power back to three-phase AC power having a form suitable to a desired application. A controller controls the inverter in a manner calculated to provide power having a waveform desired for consumption.
Specifically, the inverter includes a plurality of switches that can be controlled to link and unlink the positive and negative DC buses to motor supply lines. The linking-unlinking sequence causes voltage pulses on the motor supply lines that together define alternating voltage waveforms. When controlled correctly, by a pulse width modulator (PWM) controller, the waveforms cooperate to generate a rotating magnetic field inside the motor stator core. In an induction motor, the magnetic field induces a field in motor rotor windings. The rotor field is attracted to the rotating stator field and thus the rotor rotates within the stator core. In a permanent magnet motor, one or more magnets on the rotor are attracted to the rotating magnetic field. The rectifier, inverter, and control circuitry are commonly referred to as a motor drive unit.
The output of the motor drive unit often includes an output filter in the form of a reactor designed to reduce the peak voltages applied to the motor terminals so that reflected waves are controlled or reduced. These filters are particularly important when the distance between the output of the motor drive unit and the motor input is significant because power stability issues raised by reflected waves are further exacerbated over these long distances.
Beyond filters, it is often desirable to include a transformer between the filter and the motor inputs to isolate the motor from the utility supply and/or to step up or step down the fundamental voltage supplied by the motor drive unit to be usable by the motor. Furthermore, the transformer may be used to reduce common mode noise present on the motor supply lines.
In this regard, for convenience and serviceability, industrial/commercial motor systems are typically separated into two localities. First, the motor drive unit and filter are generally located in an area near the location where the utility lines deliver power to the facility housing the motor system. In this regard, by arranging the majority of the power “conditioning” components (i.e. motor drive unit, filter, and the like) at a centralized location near the terminal end of the utility lines, human exposure to these high power components can be reduced and servicing procedures streamlined. Second, the transformer and motor are generally located in an area proximate to the motor load. By localizing the transformer and motor components near the motor load, power losses associated with delivering power in a form suitable for driving the motor over long distances are reduced.